I can only recall one "bad" experience that we had on a Disney trip and it was about 5 years ago or something.
We had done a DVC tour and were being driven to Epcot by a CM so we could go to our ADR. On the way there, the CM was complaining about everything. I mean EVERYTHING. He started complaining that
MNSSHP was starting earlier and earlier with each passing year and he was upset they were starting that night. We failed to let him know we were going to it that night. He started complaining about other things. Then he randomly started complaining about some sort of tax somewhere. Somehow we moved on to what my husband did for a living and he managed to find something to complain about that....just on and on and on. Now, I don't want to give the impression that it really bothered us. It actually didn't. We were eager to see what next topic we could come up with to find out what complaints he had. It was almost a game to us. When we arrived at Epcot and got out of the van, we started laughing hard. It is now an occasional joke between us to just go off on complaining rants about the most random thing. Yet I know I'd be seeing people say how that CM ruined their vacation or something similar had they been in that position.
Moral of the story? Don't let every get under your skin. Even a bad attitude cast member can have a silver lining. If you let everything get to you, you are going to have a bad time. I would rather look for the positive than focus on the negative and complain.